A method of enabling entry of data into a computer system via a printed substrate. The substrate has a surface containing human-readable information and machine-readable coded data. The coded data is indicative of an identity of the substrate and of a plurality of reference points on the surface. The method includes the steps of: operatively positioning a sensing device relative to the surface and sensing the coded data; generating indicating data using the sensed coded data; and sending the indicating data to a computer system. The coded data comprises an IR-absorbing dye having a nitrogen-substituted phthalocyanine.